However, Carin Meier’s Living Clojure is excellent in many ways. Get it from O’Reilly (we’re an affiliate):

My little tutorial started with part zero, in which I lamented how functional programming is made to appear unlearnable by mere mortals, and it kind of snowballed from there. Hope you like it and/or find it useful!

In my recent post Functional Programming Without Feeling Stupid I took a quick look at how functional programming can be a little off-putting for the non-initiated. I promised to provide some examples of my own first steps with FP, and now I would like to present some to you.

Advocates of functional programming often refer to increased programmer productivity. At least some of that can be attributed to the REPL, or the Read-Evaluate-Print Loop. We are basically talking about an environment which accepts and parses any code you type in, and gives you a place to experiment and see results quickly. Before interpreted or semi-interpreted languages like Python, Java and JavaScript became mainstream, the typical repeating cycle in software development was Compile-Link-Execute, and debugging meant observing special output on the console. In the 1990s integrated debuggers with watches and breakpoints became the norm, but long before that Lisp-like languages already had a REPL, and Python also acquired one.

If you are thinking about getting intimate with Clojure, you will need to get to know the REPL. It is your playground, and will always be, even if you later start packaging and organizing your code.

Clojure depends on the Java Virtual Machine (JVM) and is actually distributed as a normal JAR file (Java ARchive), like most Java libraries are. You can start Clojure from the JAR, but you will save yourself some trouble and prepare for the future if you install Leiningen, the dependency management tool for Clojure. It is simple to install and run, and I will assume that you will follow the instructions on the Leiningen web site sooner or later. Now would be a good time.

When you’re done with the installation, you only need to say

lein repl

to start a Clojure REPL. I’m using OS X, so what I describe here was done from Terminal. You don’t need to create a project with Leiningen if you just want to play around in the REPL.

Of course, if you don’t have Java installed, you need to get it first. Refer to the Java web site of Oracle for details as necessary. Furthermore, some of the things I will describe require Java version 7 or later.